As part of ongoing evolution of the Wideband Code Division Multiple Access (WCDMA) standard in Release 8 of the Third Generation Partnership Project (3GPP) standard, a new work item was established to incorporate an enhanced dedicated channel (E-DCH) for wireless transmit receive units (WTRUs) in a CELL_FACH state.
FIG. 1 shows radio resource control (RRC) service states of a 3GPP WTRU with an enhanced uplink (UL). The WTRU may operate in several states depending on the user activity. The following states have been defined: IDLE, cell dedicated channel (CELL_DCH), cell forward access channel (CELL_FACH), universal mobile telecommunications system (UMTS) terrestrial radio access network (UTRAN) registration area paging channel (URA_PCH), and cell paging channel (CELL_PCH). RRC state transitions are controlled by the network using radio network controller (RNC) parameters, in general the WTRU does not decide to perform state changes by itself.
In the CELL_DCH state, a dedicated physical channel is allocated to the WTRU in the UL and the downlink (DL). The WTRU is known on a cell level according to its current active set. The WTRU may use dedicated transport channels, shared transport channels, or a combination of these transport channels.
A WTRU is in the CELL_FACH state if it has been assigned to use the common channels (e.g., forward access channel (FACH), random access channel (RACH)). In the CELL_FACH state, no dedicated physical channel is allocated to the WTRU, and the WTRU continuously monitors a forward access channel (FACH) (e.g., carried over the secondary common control physical channel (S-CCPCH)) or a high speed downlink shared channel (HS-DSCH) in the DL. The WTRU is assigned a default common or shared transport channel in the UL (e.g., random access channel (RACH)) that it may use anytime according to the access procedure for that transport channel. The position of the WTRU is known by the UTRAN on a cell level according to the cell where the WTRU last performed a cell update.
In the CELL_PCH state, no dedicated physical channel is allocated to the WTRU. The WTRU selects a PCH, and uses discontinuous reception for monitoring the selected PCH via an associated page indicator channel (PICH). No UL activity is possible. The position of the WTRU is known by the UTRAN on a cell level according to the cell where the WTRU last performed a cell update in the CELL_FACH state.
In the URA_PCH state, no dedicated channel is allocated to the WTRU. The WTRU selects a PCH, and uses discontinuous reception for monitoring the selected PCH via an associated PICH. No UL activity is possible. The location of the WTRU is known on a UTRAN registration area level according to the URA assigned to the WTRU during the last URA update in the CELL_FACH state.
The RACH transport mechanism is based on a slotted-Aloha approach with an acquisition indication. Before transmitting a message, a WTRU acquires the channel by transmitting a short preamble that is made up of a randomly selected signature sequence in a randomly selected access slot. The WTRU then listens and waits for an acquisition indication from a Node-B on the acquisition indication channel (AICH). The indication includes a specific AICH signature sequence mapped one-to-one to the preamble signature sequence chosen by the WTRU. If a positive acquisition indication is received, the WTRU has effectively acquired the channel, and may transmit its message. The resources that the WTRU may use in the RACH systems are predetermined by the choice of the preamble signature sequence.
The E-DCH may be used to increase the data rate for CELL_FACH WTRUs in a new enhanced RACH (E-RACH). The WTRU may transmit via the E-DCH for a longer duration than is possible using the Release 99 RACH (i.e., 10 ms or 20 ms durations).
Transmission over E-DCH requires dedicated radio control channels to be established. In pre-Release 8 systems, when moving from the CELL_FACH state to the CELL_DCH state, a synchronization procedure is executed whereby the transmit power of the Node-B and the WTRU are set to the appropriate level. This synchronization procedure A, defined in the 3GPP standards, is designed to accommodate long connection time. The procedure consists of two phases. During the first phase, only in-sync primitives may be reported from the physical layer to the Layer 3 (L3) of the WTRU. An in-sync primitive is reported if the quality of the DL radio link (RL) (i.e., fractional dedicated physical channel (F-DPCH) or dedicated physical control channel (DPCCH)) during the previous 40 ms is above a predefined threshold. Primitives are reported every 10 ms frames. The physical channel is considered established when N312 consecutive in-sync are reported in a duration period of T312, where both N312 and T312 may be configured by the UTRAN. When the physical channel is established, the WTRU may start an UL transmission. Phase 2 begins 160 ms after the physical channel is established, at which point both in-sync and out-of-sync primitives may be reported to the L3 of the WTRU.
In the case of an E-DCH transmission in the CELL_FACH state, another synchronization procedure (e.g., synchronization procedure AA) which makes use of the post-verification period is provided. The post-verification period is a 40 ms time period wherein the DL signal quality is confirmed. During the post-verification procedure, the WTRU may transmit data on the UL immediately. While transmitting, the WTRU monitors the quality of the transmission power control (TPC) field of the F-DPCH. If after the first 40 ms the quality of the TPC field of the F-DPCH is better than a threshold Qin, then the post-verification is successful, otherwise it has failed.
When the post-verification period fails for a WTRU in or moving to CELL_DCH state, the WTRU's behavior of the synchronization procedure is defined in the 3GPP standard. However, the WTRU's behavior is not defined for the proposed synchronization procedure for the WTRU when it is operating in the CELL_FACH state.
Current specifications for the RL establishment and power control are defined for dedicated RL resources that are reserved for long periods of time to a particular WTRU. However, they are not well suited for situations where the WTRU occupies the channel for short periods of time, (e.g., for burst traffic), followed by a release of the radio resources.
In the current 3GPP standard, RL failure is only triggered when the WTRU is in the CELL_DCH state. The WTRU's behavior after the RL failure includes transitioning to the CELL_FACH state, performing cell reselection and initiating a cell update procedure. However, procedures are desired for triggering an RL failure for a WTRU that is in the CELL_FACH state.